Process for simultaneous turpentine recovery and odor control

ABSTRACT

VAPOROUS RELIEF GASES FROM THE FLASHERS AND THE CHIP PREHEATERS USED IN THE STANDARD KRAFT PULPING PROCESS ARE DIRECTED TO A DIGESTER CONDENSER; VAPOROUS RELIEF GASES FROM THE EVAPORATORS OF SAID PROCESS ARE DIRECTED TO CONDENSING APPARATUS; THE FORMER GASES ARE PARTIALLY CONDENSED IN THE DIGESTER CONDENSER AND THE CONDENSATE THEREFROM IS COMBINED WITH PART OR ALL OF THE CONDENSATE FROM THE EVAPORATOR CONDENSING APPARATUS AND BOTH OF THESE ARE DIRECTED TO A STEAM STRIPPER. THE UNCONDENSED GASES FROM THE DIGESTER CONDENSER ARE CONDENSER ARE CONDUCTED TO THE CONDENSING SYSTEM OF THE STRIPPER WHERE THESE GASES ARE CONDENSED TOGETHER WITH VAPOROUS GASES ARISING FROM THE STRIPPER. FOLLOWING THIS SIMULTANEOUS CONDENSATION OF THE TWO SOURCES OF GAS, THE TURPENTINE IS RECOVERED AND THE ODOROUS FOUL GASES ARE DIRECTED TO EQUIPMENT FOR THEIR DESTRUCTION TOGETHER WITH UNCONDENSED GASES FROM THE EVAPORATOR CONDENSING APPARATUS.

July 10, 1973 J. H. FISHER 3,745,063

PROCESS FOR SIMULTANEOUS YURPE'JNTINE RLCOVERY AND OIJOI. CKJN'HIOI- Filed Nov. 1, 1971 2 Sheets-Shcnv 1 CHIPS COOKING LIQUOR couruvuous DIGESTER PRESSURE 555; FLASH TANK WASHING L L n LIQUOR /.I2

coox o CHIPS EVAPORATOR CONDENSATES T0 PROCESS CONCENTRATED BLACK LIQUOR July 10, 1973 J. H. FISHER 3,745,063

A PROCESS FOR SIMULTANEOUS TURPENTINE RECOVERY AND ODOR CONTROL Filed Nov. 1, 1971 2 Sheets-Sheet f1 STEAM S TRIPPE R CONDENSATE ODOR DES TRUCTION EQUIPMENT DIGESTER CONDENSER UOZQUJZ HUIIW United States Patent 3,745,063 PRQCESS FOR SEMULTANEOUS PEN'HNE a EtTO'VERY AND ODOR CGNTROL John H. Fisher, Vancouver, British (Columbia, Canada,

assignor to British Columbia Forest Products Limited,

Vancouver, British Columbia, Canada Filed Nov. l, 1971, Ser. No. 194,471 Int. Cl. D214: 11/06, 11/08 US. Cl. 162-15 13 Claims ABSTRACT OF THE DESCLOSURE Vaporous relief gases from the flashers and the chip preheaters used in the standard kraft pulping process are directed to a digester condenser; vaporous relief gases from the evaporators of said process are directed to condensing apparatus; the former gases are partially condensed in the digester condenser and the condensate therefrom is combined with part or all of the condensate from the evaporator condensing apparatus and both of these are directed to a steam stripper. The uncondensed gases from the digester condenser are conducted to the condensing system of the stripper Where these gases are condensed together with vaporous gases arising from the stripper. Following this simultaneous condensation of the two sources of gas, the turpentine is recovered and the odorous foul gases are directed to equipment for their destruction together with uncondensed gases from the evaporator condensing apparatus.

The present invention relates to the recovery of turpentine and the simultaneous separation and destruction of malodorous sulphur gases from the kraft process of pulp manufacture in order to prevent discharge of each of these to the environment, and to recover turpentine for sale.

In the conventional continuous kraft pulping process which employs continuous counter-current diffusion washing within a digester, the spent pulping liquor, known as black liquor, discharges continuously from the digester and is conducted to flash tanks (usually two) where the superheated black liquor flashes in steps to atmospheric pressure. The steam, which is discharged from these flash tanks, carries with it turpentine vapors, foul reduced sulphur containing gases and other non-condensable gases. The steam from the first flash tank under super-atmospheric pressure is usually conducted to the pressurized chip presteamer of the digester where some of the steam condenses to heat the chips. This presteamer is continuously vented, the vent gases consisting of considerable uncondensed steam, the turpentine and gases which accompanied the steam from the pressure flash tank, and other gases which arise from this chip presteamer. These other gases include considerable amounts of air which enters the vessel with the chips and some additional turpentine which is steamed out of the chips. This prestearner vent gas, together with the contaminated steam from the second or atmospheric flash tank, is conducted to a condenser called the digester condenser. I

In a conventional mill this condenser is operated so as to condense substantially all the steam in these gases, and the gases discharging from the condenser consist chiefly of foul sulfur gases, residual turpentine vapors and other non-condensable gases. Some of the turpentine is condensed along with the steam; the proportion going with the vent gases compared to that with the condensate depending upon the temperature of the vent gases and the amount of non-condensable gases entering the condenser. Such a system is unsatisfactory with respect to turpentine recovery.

It has been realized that the air in these gases interferes 3,7453% Patented July lit), 11973 with the condensation of the turpentine and it atfects the quality of the turpentine. It has been calculated that in a kraft mill producing 550 tons per day of kraft pulp (AD. unbleached basis) the air in this gas mixture amounts to about 12 lbs. per min. Consideration of the vapor pressure of turpentine shows that the temperature of the exit gases must be low, otherwise much of the turpentine will be in vapor form and will be lost with these vent gases. On the other hand, it is undesirable to operate the digester relief condenser to produce a cold condensate, because this makes for poor separation of the turpentine from the condensate in the following turpentine separator, if turpentine is to be recovered from this condensate in a simple phase separator following condensation. In some pulp mills the turpentine is not separated from this foul condensate and it is discharged directly to sewer since it is too foul to be used in the process. This contaminates the receiving body of water. In some mills the gases from this condenser are vented to atmosphere causing air pollution.

The other major sources of malodorous gases and foul condensate are the evaporators. In a typical multiple-effect black liquor evaporator, the condensates arising from all but the lowest pressure effect are sufficieutly low in foul materials that they may be reused directly in the pulp making process. The condensate from the lowest pressure effect, that is the condensate from the evaporator condenser, is the foulest and cannot normally be used in the process. It is normally either sewered, which contaminates the receiving body of water, or it is processed in a steam or air stripper together with the digester condensate to remove the foul gases after which the condensate can normally be used in the process. If a steam stripper is used, turpentine may be collected but such turpentine is extremely foul and of doubtful value unless the steam stripping operation makes special provision for avoiding condensation of large amounts of higher boiling sulphur compounds, as is done in the present invention.

In some mills two evaporator condensers are used in series, the first condensing the majority of the steam and the second all the remaining steam, which can be practically condensed at the low pressure used in the last evaporator effect. The first condensate is usually of suiticient quality that it may be combined with that from the other effects for reuse in the process; provided that it is not over about 70% of the total steam from the last effect. The remaining condensate from the second condenser is very foul. If a steam jet vacuum-producing system is employed, there are also condensates from the inter-condenser and the after-condenser thereof. These are also very foul.

Thus in a kraft mill equipped with a continuous digester with internal washing, with external diffusion washing as a final washing step, with a recovery furnace which avoids direct contact evaporation of black liquor, the significant sources of odor and foul turpentine are limited to the following four sources:

(1) Vent gases from the digester condenser.

(2.) Ven gases from the evaporator ejector.

(3) Foul condensate from the digester condenser.

(4) Foul condensate from the evaporator condensers.

In the past there have been various schemes developed by others for turpentine recovery and also schemes for collection and destruction of odorous gases. The processes used to date have often been ineflicient or complex. Seldom has high percentage recovery of turpentine been achieved where continuous chip digesters have been employed Objectives of the present invention are to achieve a high percentage recovery of turpentine, together with substantially complete collection and destruction of malodorous gases, to accomplish this by a relatively simple process using equipment which is trouble free and simple to operate with minimum labour, and to do these things at a relatively low capital and operating cost.

The present invention contemplates a process for simultaneous turpentine recovery and odor control from condensates and vaporous relief gases, which include turprentine, steam, air and odorous gases, from the digester and the evaporator systems in the standard kraft pulping of wood chips, which comprises directing vaporous gases from the flashers and chip preheaters used in the kraft pulping process to a digester condenser, partially condensing steam of the vaporous gases in the condenser, directing vaporous gases from the evaporator system to condensing apparatus, where substantially all the steam therefrom is condensed, removing uncondensed gases from the condensing apparatus, steam stripping at least some of the formed condensates in a steam stripper to separate turpentine and malodorous components from the bulk of the condensates, directing the separated turpentine, malodorous components and steam from the stripper to a stripper condensing system, conducting the residual uncondensedvaporous gases from the digester condenser to the same stripper condensing system, for the purpose of condensing and recovering the turpentine from these two sources simultaneously and separating the non-condensable gases, including odorous gases, conducting the condensate of water and turpentine to a turpentine separator, and removing the uncondensed odorous gases discharging from the turpentine condensing system.

The method of the present invention will now be de scribed in association with the accompanying drawings, in which FIG. 1 diagrammatically illustrates the basic apparatus used in the standard kraft pulping of wood chips, and

FIG. 2 diagrammatically illustrates a preferred form of apparatus for carrying out the present process.

Referring to FIG. 1 of the drawings, 10 is a continuous counter-current diifusion washing type digester into which wood chips and pulping liquor are fed. Hot black liquor from the digester is directed to pressure flash tank 11 and atomspheric flash tank 12 which are arranged in series. The steam which is discharged from these flash tanks carries with it turpentine vapors, foul reduced sulfur containing gases, and other noncondensable gases, and these are generally referred to herein as vaporous gases. The vaporous gases from the first flash tank 11 under superatmospheric pressure are conducted to a pressurized chip presteamer 15. Vaporous gases, which now include air, are taken away from the preheater by pipe 17. Vaporous gases from the second flash tank 12 are moved therefrom through pipe 18. The black liquor from the second flash tank 12 is conveyed to multiple effect evaporator indicated at 20. The condensates arising from all but the lowest pressure effect of the evaporator are usually sufliciently low in foul materials that they may be reused directly in the pulping process. The vapors from the lowest pressure effect of the evaporator are removed therefrom through a pipe 22. The condensate from these vapors is foul and is not usually used in total in the pulp mill.

By referring to FIG. 2, it will be seen that the vaporous gases from pipes 17 and 18 are directed into a digester condenser 25. The vapor from evaporator 20 is directed through pipe 22 to condensing apparatus which, in this example, comprises vacuum condensers 28 and 29 connected in series.

The digester condenser 25 is instrumented so as to cause only a portion of the steam in the vaporous gases to condense, for example, about 80%. The uncondensed vaporous gases, which contain most of the turpentine, foul gases and air arising from the digester system, are removed from condenser 25 through pipe 32. The condensate is directed through pipe 33 to a seal tank 34. All or part of this condensate may alternatively be directed to some other place in the pulping process if a suitable use can be found for this contaminated hot condensate. The degree of contamination or foulness of this condensate depends largely on the proportion of steam condensed in the digester condenser 25.

The condensate from condenser 28 is usually clean enough to be reused in the pulping process. The condensate from condenser 29 is directed to tank 34, but part or all of that from condenser 28 may also be directed to tank 34 if desired. The vaporous gases from condenser 29 having been compressed to atmospheric pressure through steam ejectors 35 and 36 with interstage condenser 37 therebetween, are directed through a scrubber 38 to an efiicient after condenser 39. In this example, the evaporator condensing apparatus includes condensers 28, 29, 37 and 39. The scrubber 38 is not an essential feature of this invention, but if one is used it should be operated with hot alkaline liquor (usually white liquor from the kraft mill) preferably above about 140 F. This minimizes the condensation of turpentine in this scrubber. Most of the turpentine which enters the evaporator system in the black liquor, emerges in the vapor from the lowest pressure effect and it leaves the system largely in the foul condensate from the second evaporator condenser 29 and in the condensates from condensers 37 and 39 provided that the scrubbing liquid is maintained above about 140 F. and provided that the condenser 39 cools the gas to about 70 F. or lower. In this way loss of turpentine to the alkaline scrubbing liquid is minimized as well as loss in the vapors leaving condenser 39. Thus most of the turpentine entering the evaporator system leaves in the three condensates from condensers 29, 37 and 39, and these condensates are all directed to tank 34. The gases from condenser 39 pass to a collector 40, whence they travel to any known type of destructive system, indicated at 41.

Any condensate from collector 40 is also directed into tank 34. The condensates are directed from tank 34 to the heat exchanger 47 of a steam stripper 48 where the turpentine is recovered.

The vaporous gases from condenser 25 are conducted by pipe 32 to heat exchanger 47 where they elevate the temperature of the condensates supplied thereto through pipe 45. The amount of steam in the gases discharging from condenser 25 is adjusted in accordance with the flow and temperature of the foul condensate entering exchanger 47. The amount should be somewhat more than suflicient to heat the foul condensate to close to the boiling point on discharge from the exchanger to the top of stripper 48, because of the presence of non-condensable gases in the vaporous gases entering the heat exchanger. This quantity of steam should be about 50 to 100% more than that theoretically required to heat the incoming condensate to the boiling point. More can be used if desired, especially if it is elected not to strip the foul condensate from the digester condenser. However, it is undersirable to use all of the hot gases from the digester in the heat exchanger because this would necessitate the latter being unnecessarily large, and also would cause too much condensate to form in the primary turpentine condenser, to be described later. This would undesirably raise the ratio of condensate to turpentine in the turpentine condensing and separation system. As an example, if some of the steam in the vaporous gases is condensed in condenser 25, the remaining 20% will usually be suflicient for heating the condensate and with some to spare, providing that only a minor fraction of the condensate from the evaporator condensers goes to the stripper. If, however, it is elected to direct all the condensate from the evaporator condensing system to the stripper 48, then considerably more steam will be required to be left uncondensed in the vapors discharging from the condenser 25. In that situation the resulting smaller fiow of condensate from condenser 25 may be sufiiciently clean to make its stripping unnecessary and to allow its use directly elsewhere in the pulping process. Thus there is considerable flexibility in the operation of condenser 25 depending on how the evaporator condensor 28 and 29 are operated and on the process requirements elsewhere for condensate from condenser 25. If this condenser is operated in the manner described in this invention, the condensate is discharged at a temperature very close to the boiling point and it is therefore a potentially valuable condensate for use in the kraft pulping process because of its heat content.

The steam which enters the base of stripper 48 passes upwardly through this stripper, removing turpentine and dissolved gases by counter-current stripping. Sufiicient steam condenses during its passage to heat the condensate to very close to the boiling point at any given stage of the stripper. Some steam must discharge from the top of the stripper in order to accomplish any stripping action, and the efiiciency of the stripper is related to the ratio of the condensate feed to this steam discharge, and to other factors entering into the design of the stripper, as is well known to those skilled in the art of stripper design. However, for any given stripper size and design and for given conditions of condensate feed and steam flow to the stripper base, the overall efiiciency of the stripping action is improved by passage of the vapors from condenser 25 through heat exchanger 47 together with the steam and vapors discharging from the top of the stripper. The presence of air in these gases has disadvantages and advantages. The disadvantage is that it makes the recovery of turpentine more difficult in the condensers of the turpentine recovery system. The advantage gained from the present invention is that the air assists in the carry-through of odorous reduced sulfur compounds out of the turpentine condensers and through to the odor destruction system. This is especially true of higher boiling reduced sulfur compounds, such as dimethyl sulfide and dimethyl disuhide. If a steam stripper were to process foul condensates without the introduction of gases from the digester condenser into the condensing system, these high boiling sulfur compounds would remain to a much larger degree with the turpentine, thus diluting and highly contaminating it so that the turpentine would be less saleable. Air can be introduced in a stripper system which does not integrate with the digester gases, but if such integration is not practiced, as is done in the present process, then a separate additional turpentine collecting system must be installed to recover the turpentine from the digester vapors, and in such a system the problems associated with the presence of air are encountered. One of the advantages of the present process is that all the turpentine from both digester and evaporators is collected in one system, good steam economy is achieved, and the total equipment required is reduced and simplitied while at the same time producing a superior quality turpentine.

The condensate from digester condenser 25 is hot, usually near the boiling point, but the condensates from condensers 29 and 39 are cooler, usually about 130 F., and hence require to be heated before entering stripper 48 for steam economy. The condensates having passed through the stripper are sufficiently reduced in sulfur gases and turpentine that they can be used in the kraft pulp mill where very hot water can be used to best economic advantage. The quality depends on the amount of stripping steam used.

The turpentine, odorous reduced sulfur gases and other non-condensables discharging from heat exchanger 47 are conducted along with steam to the primary turpentine condenser 52. The cooling water for this condenser is instrumented in such a way as to discharge the condensate hot, preferably between 150 and 190 F. Even at the higher temperature, the bulk of the steam is condensed. The gases from condenser 52 are conducted to secondary condenser 53. The important function of this secondary condenser is to condense the turpentine. A high temperature is desired in the bulk of the condensate from condenser 52 for two reasons, namely,

6 1) for heat economy, since it is returned to the top of the stripper and must be reheated eventually to near boiling point, and (2) to aid in turpentine separation since the solubility of turpentine reduces with temperature.

0n the other hand, the temperature of the gases must finally be reduced to the lowest practical level before leaving secondary condenser 53 in order to condense the maximum turpentine. Consequently, the secondary condenser must be efficient and must use the coldest available water. The condensate from this condenser will be cold and, therefore, it is desirable to minimize this flow and take out the bulk of the steam in the primary condenser 52. The condensates from condensers 52 and 53 are combined and passed through the turpentine separator 55 where the turpentine floats and continuously discharges from the upper discharge port thereof, and the aqueous phase continuously discharges from the lower port back to stripper d8. Appropriate pressure equalizing lines are arranged on this equipment, and a seal pot S8 is used through which the condensate passes back to the stripper in order to facilitate the continuous discharge of the fluids from separator 55 and to maintain the turpentine condensate interphase in any desired position.

An alternative method of operation is to pass part or all of the hot condensate from the turpentine condenser 52 directly back to the stripper exchanger 47. This permits the use of a smaller turpentine separator or, for any given size separator, allows the dwell time to be increased. The portion of the flow from condenser 52 which is by-passed directly to exchanger 47 can be adjusted in the field as well as the temperature of this condensate in order to achieve the best performance in the turpentine separator.

Heat exchanger 47 is part of the stripper condensing system. It can be made integral with the stripper, if desired, in which case it is an extension of the stripping column. It is shown separately in FIG. 2 to illustrate that it is primarily a condensing direct contact heat exchanger. If steam economy is of little importance, the vapors from digester condenser 25 may, alternatively, be conducted directly to the primary turpentine condenser 52. The advantages mentioned above relating to improving the quality of the turpentine will still be realized. However, an important feature of this invention is that the digester condenser gases be mixed With the gases from the stripper and all condensed in the same condensing system.

In the diagram of FIG. 2 the parts of the stripper condensing system are, exchanger 47 and condensers 52 and 53. There is considerable flexibility of design in the stripper condensing system, depending on the steam economy required and the cooling water available, and the desired temperature of the warm Water discharging from the condensing system. Thus, if desired, condensers 52 and 53 may be combined into one condenser, provided that the coldest practical temperature of discharge gases is achieved. Since it is desirable also to produce a warm condensate, preferably F. or higher, a vertical condenser is desirable if a single condenser is used. In this the vapors enter the bottom of the condenser and flow upwardly countercurrent to the downcoming condensate. Counter-current flow of the cooling water would be required and the coldest available cooling water should be used. Thus, in the simplest form, the stripper condenser system may be only one vertical condenser arranged in this matter. This would not give the best steam economy nor the easiest method of control of condensate temperature. Therefore, it is preferable to have the first condensing unit as a direct contact exchanger 47, and it is preferred to make the surface condensers in two parts as shown, condensers 52 and 53, for ease of control and also to allow the use of warm water as cooling water in the primary condenser, and this produces a hotter Water from this condenser for use in the kraft process elsewhere. This arrangement also allows for more flexibility as to temperature of the first condensate and the possibility of by-passing part or all of this directly back to the stripper.

The arrangement of the stripper condensing system may be varied considerably as aforesaid according to the needs of the mill without departing from the essential feature of this invention which is to conduct residual steam and accompanying gases from the digester condenser to some part of the stripper condensing system.

The foul gases discharging from the secondary turpentine condenser 53 are conducted to the common seal tank 40 where they are mixed with the evaporator foul gases and conducted from there to the destructive device 41. The destructive device may be the lime kiln of the kraft mill. Alternatively, the foul gases may be conducted to an incinerator. There is some preference for the lime kiln since S formed on burning the foul gases is largely absorbed in the kiln system and is returned to the kraft process liquors instead of being discharged to atmosphere, as is the case With a separate incinerator, unless such separate incinerator has a scrubbing system, which makes for an expensive, complicated system. However, the foul gases may be destroyed in any desired or convenient manner.

An ejector 60 is shown between condenser 53 and collector 40. This is not an essential feature of the present process, but may be required in some installations where it is desirable to limit the pressure out the exit of the digester condenser to approximately atmospheric pressure. In that case, some device, is necessary to create a small pressure increase in order to overcome the line pressure drop through the piping and equipment. An ejector has the advantage that it is also an excellent flame arrestor. Conventional flame arrestors should be placed also at other appropriate places and the instrumentation should be arranged so as to minimize the risk of flame propagation from the odor destruction unit 41, as will be apparent to those skilled in the design of equipment for handling potentially explosive gases.

This is a comprehensive process whereby the turpentine from all the significant sources in the kraft mill is recovered in one turpentine condensing system, system also serves to collect and separate the combined off-gases from the digester and from the stripping of all foul condensates, and furthermore accomplishes this collection and separation while at the same time improving the quality of the turpentine. In this process, vaporous relief gases from the flashers and the chip preheaters used in the standard kraft pulping process are directed to a digester condenser; vaporous relief gases from the evaporators of said process are directed to condensing apparatus; the former gases are partially condensed in the digester condenser and the condensate therefrom is combined with part or all of the condensate from the evaporator condensing apparatus and both of these are directed to a steam stripper. The uncondensed gases from the digester condenser are conducted to the condensing system of the stripper Where these gases are condensed together with vaporous gases arising from the stripper. This simultaneous condensation of the tWo sources of gas not only makes for economy in the provision of common equipment for condensing and turpentine separation but also improves the quality of the turpentine recovered because the presence of considerable amounts of noncondensable gases in the residual gaseous vapors discharging from the digester condenser helps to carry oil? high boiling odorous sulphur compounds in the non-condensable gases for subsequent destruction, which sulphur compounds would otherwise tend to remain with the turpentine with consequent lowering of quality. If a direct contact heat exchange section is provided at the top of the stripper these gases from the digester condenser may be introduced to the stripper condensing system at this point thus elevating the temperature of the condensates being directed to the stripper and simultaneously aiding in the stripping action. This is the preferred manner of opera- 8 tion. The condensate of water and turpentine formed in th stripper condensing system is directed to a turpentine separator for turpentine recovery and the odorous aqueous condensate phase is returned to the stripper head. The noncondensable gases having been reduced to the lowest practical temperature in the condenser system in order to effect the maximum turpentine recovery, are then directed to standard equipment for destruction of the odorous components of these gases.

The process may also be operated by stripping only the condensate from the evaporators provided that a suitable use can be found in the pulping process for the near boiling condensate arising from the partial condensation of the gases to the digester condenser and providing that the proportion of steam condensed in the digester condenser is limited sufliciently to produce a condensate of usable quality.

I claim:

1. A process for simultaneous turpentine recovery and odor control from vaporous relief gases and condensates from the digester and evaporator systems in the kraft pulping of wood chips, which comprises directing vaporous gases from the flashers and chip preheaters used in the kraft pulping process to a digester condenser,

partially condensing steam of the vaporous gases in the condenser,

directing vaporous gases from the evaporator system to condensing apparatus, where substantially all the steam therefrom is condensed,

removing uncondensed gases from the condensing apparatus,

steam stripping at least some of the formed condensates in a steam stripper to separate turpentine and malodorous components from the bulk of the condensates,

directing the separated turpentine, malodorous components and steam from the stripper to a stripper condensing system,

conducting the residual uncondensed vaporous gases from the digester condenser to the same stripper condensing system, for the purpose of condensing and recovering the turpentine from these two sources simultaneously and separating the non-condensable gases, including odorous gases,

conducting the condensate of water and turpentine to a turpentine separator, and

removing the uncondensed odorous gases discharging from the turpentine condensing system.

2. A process as claimed in claim 1 in which the removed uncondensed gases from the condensing apparatus and from the turpentine condensing system are conducted to odor destruction equipment.

3. A process as claimed in claim 1 in which condensates from both the digester condenser and the evaporator condensing apparatus are stripped in the steam stripper.

4. A process as claimed in claim 1 in which said strip per condensing system includes a direct contact heat exchanger into which the gases from the digester condenser, the gaseous discharge from the stripper and said condensates are directed, whereby the temperature of said condensates is elevated.

5. A process as claimed in claim 3 in which said stripper condensing system includes a direct contact heat exchanger into which the gases from the digester condenser, the gaseous discharge from the stripper and said condensates are directed, whereby the temperature of said condensates is elevated.

6. A process as claimed in claim 1 in which said condensing apparatus comprises first and second vacuum condensers in series, condensate from the second condenser being directed to the steam stripper, and compressing vaporous gases from the second condenser, condensing substantially all the residual steam and turpentine in the compressed vaporous gases, directing the condensates to the steam stripper, and conducting the uncondensed gases to odor destruction equipment.

7. A process as claimed in claim 3 in which said condensing apparatus comprises first and second vacuum condensers in series, condensate from the second condenser being directed to the steam stripper, and compressing vaporous gases from the second condenser, condensing substantially all the residual steam and turpentine in the compressed vaporous gases, directing the condensates to the steam stripper, and conducting the uncondensed gases to odor destruction equipment.

8. A process as claimed in claim 4 in which said condensing apparatus comprises first and second vacuum condensers in series, condensate from the second condenser being directed to the steam stripper, and compressing vaporous gases from the second condenser, condensing substantially all the residual steam and turpentine in the compressed vaporous gases, directing the condensates to the steam stripper, and conducting the uncondensed gases to odor destruction equipment.

9. A process as claimed in claim 5 in which said condensing apparatus comprises first and second vacuum condensers in series, condensate from the second condenser being directed to the steam stripper, and compressing vaporous gases from the second condenser, condensing substantially all the residual steam and turpentine in the compressed vaporous gases, directing the condensates to the steam stripper, and conducting the uncondensed gases to odor destruction equipment.

it). A process for simultaneous turpentine recovery and odor control from vaporous relief gases, such as turpentine, steam, air and other gases, from digesters, flashers, chip preheaters and evaporators in the standard kraft pulping of Wood chips, which comprises directing vaporous gases from the flashers and preheaters to a digester condenser,

partially condensing the steam of the vaporous gases in the condenser,

directing vaporous gases from the evaporator to condensing apparatus,

directing condensates from the digester condenser and the condensing apparatus to a heat exchanger in communication with the top of a steam stripper, directing the hot uncondensed gases of the digester condenser together with the gaseous discharge from the stripper to said heat exchanger to elevate the tem- 1G perature of the condensate in the latter, steam in the stripper removing turpentine and dissolved gases from said condensate therein by counter-current stripping, conducting the vaporous gases from the stripper heat exchange to a condenser, and

directing the condensate from the last-mentioned condenser to a turpentine separator.

11. A process as claimed in claim 10 including removing malodorous gases from said last-mentioned condenser for destruction and also removing uncondensed malodorous gases from the evaporator condensing apparatus for destruction.

12. A process as claimed in claim 10 in which said condensing apparatus comprises a vacuum condensing system and an after condenser, and passing vaporous gases from the vacuum condensing system through a scrubbing system to remove sulfur compounds therefrom before directing said gases to the after condenser, removing malodorous gases from the after condenser for destruction, and directing condensate from the after condenser to said stripper heat exchanger.

13. A process as claimed in claim 10 in which said condensing apparatus comprises two condensers in series, and including directing condensate from the first of said condensers back to the pulping process, and

directing the condensate from the second of said condensers to said steam stripper.

References Cited UNITED STATES PATENTS 3,432,402 3/ i969 Herrlinger et a1 162-16X 1,942,767 1/1934 Oman et al 203-96 3,028,295 4/1962 Trubeck et a1 162-51 3,183,145 5/1965 Collins, Ir. 162-51 X 3,311,531 3/1967 Feischl et al. 162-51 FOREIGN PATENTS 673,649 1/ 1930 France.

S. LEON BASHORE, Primary Examiner R. V. FISHER, Assistant Examiner US. Cl. X.R. 

